I'm trying to use motion sketch and write on to create a signature (using the position values from Motion Sketch layer to control the position of paint brush on Write On layer).

What's the best way to cross the letter T or dot an i?

With motion sketch, as soon as you release the mouse button, things are terminated.

If I simply restart the motion sketch capture to cross my t, the horizontal line happens at the beginning (time 0), even if I advance the playhead /CTI to the appropriate spot (after rest of word drawn).

Is the best workaround simply to repeat the process on fresh layers to complete any discontiguous strokes and then manually position those in the timeline?

Not a big deal if I just want a re-usable signature. But if I wanted to use this on longer writing samples more routinely, it could get a bit cumbersome.

When animating a person's signature, I use masks to define a path, then apply the Write-On effect: one instance of Write-On for each contiguous piece of writing. This means that at natural pen lift points, there's a new instance of Write-On.

Animating real signatures takes some doing because it's not an automatic process at all, but it's worth doing in the end.